The display field of a display system may take the form of the screen of a device such as a cathode ray tube or a liquid crystal display, or possibly also the print field of a printer. The data for display may be stored by the display device itself as would be the case in a storage tube, or it may be held in refresh storage for, for example, a cathode ray tube device. Either way, a mechanism has to be provided in order to specify the actual location within the display field at which a particular piece of information is to be displayed. In digital systems, this is done by dividing the display field into an array of pixel positions which can be addressed. This means that the display field is quantized and raises problems in the case where an array of data values to be represented is large and consequently has a finer definition than is provided by the quantization of the display field.
One example where difficulties arise in the display of data within a display field is in the display of speech waveforms. Typically, 1 second of speech would comprise 10000 samples whereas graphic displays can at best display around 1000 pixels in the x or y direction. To display a significant portion of the speech waveform with x as the time axis, therefore, many consecutive waveform samples will have to be associated with a single x pixel position. The conventional approach to plotting the samples in the display field is to plot each of the sample values in turn in accordance with a scaling factor whereby many sample values are plotted at each pixel position along the x axis.